How Can I Remove CGI from Part of my Video?
There are two methods that this could be done with:

Movie Clip Editor and Compositor:


Add your footage to the Movie Clip Editor
Mask the area around the Light Sabre at the time you don't want it
Use the Mask node in the compositor to remove the light sabre


Section on animating masks from the Blender Documentation (Link). There are also many good tutorials on this.


  Animating
  Masks can be driven over the time so that they follow some object from the footage, e.g. a running actor. This animation can be done in several ways:
  
  Control points can be parented to motion tracks. This way is the main way to interact with masks in a motion tracking workflow.
  Keyframe animation of control points using a shape keying system. This can be useful when there are not enough good feature points to track in the footage, or the mask is not based on footage.
  For animation more complex mask shapes, it is also possible to do more high level animation:
  
  Splines and mask layers can be animated as a whole, instead of individual control points.
  
  Masks can be parented to motion tracking data. Works for both individual mask point parenting and for overall spline. To select motion track to be parented to use Ctrl-RMB. To parent selected mask points to active motion track use Ctrl-P.
  Mask animation timing can be edited from the Dope Sheet. Here there is a mask mode where mask keyframes can be selected and edited.


Animating the appearence of the 3D Model:


Open the Outliner and locate your light sabre object
Next to its name you will see an eye and camera
Animate appearence by using the keyframe shortcut I and keyframe it to the time it should be seen or hidden. This is done by hovering over the symbol (eye or camera), to hide the object click on the icons and they will become greyed out and your object should disappear.


Make sure you animate both the eye and the camera, this is beacuse the eye only hides its appearence in the viewport but will still be visible in the render.